The present invention relates to an air bag in an air bag equipment, which is expanded by reaction gas from an inflator when a vehicle is collided, and protects a person in the vehicle, and in particular to an air bag provided with an exhaust outlet to discharge the gas gradually in order to alleviate the impact when such person hits the air bag.
The air bag equipment as installed on a fixed portion of a car body in front of a car seat plays an important role for the protection of a person in the car from injury due to the collision of the car body as the air bag is instantaneously inflated at the collision of the vehicle by the pressure of reaction gas released from an inflator, which is fixed on a stearing wheel or dashboard.
In such air bag equipment 1, for example, chemical reaction of gas generating agent is induced by a collision signal from a collision detection sensor when the vehicle deceleration is higher than a predetermined level as shown in FIG. 5. It comprises an inflator 2 to inject the reaction gas, and an air bag 3, the base of which is fixed on the inflator 2 and which is inflated by the gas injected from the inflator 2. This air bag equipment is mounted on a fixed portion of a car body such as the central portion of the steering wheel 5 with the air bag folded up and accommodated in a pad 4.
As shown in FIG. 6, the gas generating agent in the inflator 2 starts the reaction when the vehicle is collided, and the air bag 3 is instantaneously expanded by the reaction gas thus generated. The air bag receives the person M, who is thrown forward by inertia, and protects him from the collision with the car body.
When the person M is collided with and received by the air bag 3 inflated at the collision of the car, the pressure in the air bag 3 is relatively high, and the impact caused by the collision is big. In order to alleviate such impact, an exhaust outlet is provided on the air bag 3. By gradually releasing high pressure gas of the air bag 3 from this exhaust outlet 6, the impact due to the collision of the person M with air bag 3 is absorbed.
In the meantime, the vehicle provided with such air bag equipment 1 is driven at various places. Specifically, the vehicle is driven in an area at high temperature such as the equatorial area or in an area at extremely low temperature such as Siberia. When the atmospheric temperature extremely differs according to the place where the vehicle is driven, the condition for chemical reaction of the gas generating agent changes according to the temperature. Thus, the reaction condition of the gas generating agent in the inflator 2 also varies. Namely, in a high temperature area, the reaction is not only quick, but the internal pressure of the air bag is high because it is inflated due to high temperature of gas, while, in a low temperature area, internal pressure of the air bag is not very high because temperature of reaction gas is low. As the result, the time required for complete expansion of the air bag 3 extremely differs according to the place where the vehicle is driven. In general, the time required for complete expansion of air bag 3 is about 30 ms at normal temperature, about 25 ms at high temperature and about 40 ms at low temperature.
On the other hand, when the vehicle speed is 48 km/h, the time from the collision of the vehicle until the person M in the vehicle hits the steering wheel 5 is about 50-70 msec and the time until the person hits the instrument panel or windshield is about 70-90 ms. This time does not depend on the atmospheric temperature.
Therefore, when the person M hits the inflated air bag after the collision of the vehicle, internal pressure of air bag 3 differs according to the temperature of atmospheric air. In other words, the time required until the complete expansion of air bag 3 is short in a high temperature area, and the internal pressure of air bag 3 is amply high when the person M hits air bag 3, whereas, in a low temperature area, the time up to the complete expansion of air bag 3 is long, and internal pressure of air bag 3 is relatively low when the person M hits the air bag 3. In this way, internal pressure of air bag 3 varies according to the temperature of atmospheric air.
When the air bag 3 is furnished with an exhaust outlet 6 as described above, a part of reaction gas introduced from the inflator 2 during the inflating process of air bag 3 is discharged from the exhaust outlet 6. This results in pressure loss, and longer time is required until the air bag is completely expanded.